Electroplating of cadmium



United States Patent ELECTROPLATKNG 0F CADMIUM Le Roy B. High and Wilbur E. Hague, Detroit, Mich., assignors, by mesne assignments, to Udylite Research (Jorporation, Detroit, Mich, a corporation of Michigan No Drawing. Application October 12, 1953,

Serial No. 385,688

6 Claims. (Cl. 20450) This invention relates to improvements in the electrodeposition of bright cadmium plate from cyanide baths. More particularly it relates to the use of certain additives for prevention of gas-pitting caused by the attachment or clinging of hydrogen bubbles cathodically released during electrodeposition, these additives being characterized by their ability to greatly minimize or prevent pitting while concurrently cooperating with other brighteners to extend the bright plating range of the cadmium cyanide bath.

In the electrodeposition of cadmium from cyanide baths, it is highly desirable to use organic addition agents which make possible fine-grained bright plate and also improve the covering power and throwing power of the cadmium into deep recesses of articles plated for corrosion protection. Many organic addition agents have been found in a period of over twenty years which can accomplish this result. For example, various proteins such as gelatin, glue, albumins, polymerized or caramelized sugars or cereals like Postum; soluble cellulosic products such as carboxy methyl cellulose, hydroxy ethyl cellulose, starch, dcxtrin, lignins, bath-soluble polymerized resins, poly-vinyl alcohol, etc. However, a major fault with some of the more colloidal of these materials is that they cause the hydrogen bubbles evolved during electrodeposition to stick or cling to the cathode, thus preventing plating at those points with the results that pits are left in the plate. Although the problem of pitting due to hydrogen bubbles clinging to the cathode is relatively unimportant in bulk or barrel plating where the tumbling action dislodges the hydrogen bubbles, in rack or still plating, pitting is a serious commercial problem.

A number of wetting agents have been heretofore proposed to overcome this problem of pitting including, for example, sodium or potassium lauryl sulfate, sodium .decyl sulfate, sodium decyl benzene sulfonate sodium isopropyl naphthalene sulfonate, sulfonated Turkeyred oil (sulfated ricinoleate) etc. However, while these Wetting agents reduce the pitting they do not concurrently cooperate with other effective organic brighteners in improving the brightness of the deposit and extending the bright plating current density range of the cyanidecadmium bath.

In accordance with the present invention it has been found that the problem of pitting can be greatly minimized, the brightness of the deposit improved and the current density range of the cyanide-cadmium bath extended by the inclusion in the bath of a sulfated dior monoleate ester, its hydrolytic product, sulfated oleic acid, or mixtures thereof. The monoleate esters of this invention may be either mono-sulfated or di-sulfated and the mono-sulfated monoleates are preferred.

The sulfated oleyl esters of this invention may be formed by conventional procedures. The desired oleic ester may be formed from any of a wide variety of alcohols including any alcohol or phenol which contains not more than two (2) hydroxy groups and not more 2,803,593 Patented Aug. 20, 1957 ICC than eight (8) carbon atoms. Typical of the alcohols which fall within this category are methyl, ethyl, propyl, butyl alcohols; ethylene, diethylene, triethylene, propylene, dipropylene, etc., glycols; ethylene chlorohydrin, ethanolamine; and the glycol ethers including ethylene glycol, monomethyl ether, ethoxyethanol, methoxyethoxyethanol, (diethylene glycol, monomethyl ether), methoxytriglycols, etc.

Because of their availability and low cost, the esters are preferred over sulfated oleic acid and especially the lower alkyl esters such as sulfated methyl oleate. In the cadmium plating bath, the alcohol portion of the sulfated esters of this invention tend to hydrolyze slowly to produce in the bath the sulfated oleic acid which is then in admixture with the sulfated oleic ester. It is also thought that di-sulfated monoleates, for example, the di-sulfated monoethylene glycol ester of oleic acid and di-sulfated dioleates, for example, the disulfated dioleate of ethylene glycol tend to produce in the bath monosulfated monoleates and it is therefore to be understood that suitable starting materials for the purpose of producing the sulfated monoleate additives of this invention also include di-sulfated monoleates and di-sulfated dioleates. It will be apparent that in the disulfated monoleates, the oleic acid portion carries one sulfate group and the alcohol portion carries the other sulfate group. The sulfated oleic acid esters of this inventionsmay also be formed by di-sulfating the oleic acid ester of oleyl alcohol and the dioleates of other glycols may be disulfated to produce the compounds of this invention as well. The various esters of this invention may be sulfated by using concentrated sulfuric acid in a range of temperature from about 0 C. to normal room temperature and it will be apparent that the esters may be formed from oleic acid or elaidic acid or if desired, 10-hydroxy stearic acid.

In order to obtain a noticeable reduction in pitting and an increase in the brightness of the deposit, it is necessary to include in the cyanide-cadmium bath a proportion of the additive of this invention in an amount of at least about 0.01 gram/liter. The optimum concentration range of the additives of this invention for use in cyanide-cadmium plating baths to obtain the maximum beneficial effect, has been found to be in the range of 0.018 to 0.3 gram/liter in the operating bath. The cyanide-cadmium plating baths which are improved by the incorporation therein of the additives of this invention may be any cyanide-cadmium bath which, upon electrolysis, produces a cadmium coating at the cathode. The beneficial effects obtained from the use of the additives of this invention have been found to apply tdthe large number of cyanide-cadmium bath compositions which are now well-known in this art. Because of this wide range of applicability to the various known cyanidecadmiuni plating baths, the particular cyanide-cadmium bath chosen may be selected by one skilled in the art to best fulfill the particular requirements of the application at hand. In general, the bath may comprise any cyanide, such as the alkali metal cyanides, and a bath-soluble cadmium compound such as cadmium oxide. Preferably, the bath will also contain a metal brightener of the group consisting of zinc, copper, iron, nickel and cobalt, and one or more of the hereinabove listed or otherwise known organic brightening agents.

The cyanide-cadmium plating bath additives of this invention, most advantageously, may be handled, transported and introduced into such baths in the form of an aqueous concentrate. A desirable concentrate for this purpose is one which contains about 25 grams to 50 grams of an additive of this invention (in strength) per gallon of the aqueous concentrate. As a oleate.

'50 grams of 100% sulfated methyl oleate per gallon of the aqueous concentrate has been found to be highly Satisfactory,

The additives, bath compositions. and. method of .this 'invention are illustrated in greater detail in the examples 'given below. Example I A stock cyanide-cadmium solution was made up hav- .ing a composition of 3.5 ounces/gallon of cadmium oxide and 14.5 ounces per gallon of sodium cyanide. To a one liter portion of this stock solution, a portion of an aqueous nickel sulfate solution was added to pro- ;duce a nickel concentration of 0.405 gram. 11.2 cc. of 2% medium viscosity hydroxy ethyl cellulose was added and the solution placed in a Hull cell. On electrolysis,a panel positioned in the Hull cell as the cathode was found to be plated on the low current density .half of the panel with a relatively bright plate containing a trace of cloudiness but the edge of the low current .density area was coated with a heavy orange peel type plate which was severely pitted. The solution was altered by adding thereto 1.9 cc. of a sulfated methyl oleate aqueous concentrate containing 2% by weight of 100% sulfated methyl oleate so that the solution contained 0.038 gram of sulfated methyl oleate. The plate on a panel, produced from this modified solution, was found to contain no orange peel or pitting along the low current density edge and the bright plate range was extended farther into the higher current density half of the panel. The brightness of the low current density half of the panel was also improved. Equivalent concentrations of sulfated ethyl, propyl, butyl and ethyl- .ene glycol oleate produce plate which is generally comparable in appearance to that obtained using the methyl ester, although the degree of brightening obtained is somewhat less than that obtained with the methyl ester.

Example II To another one liter portion of the stock solution of Example I, 0.112 gram of Darlings hide glue #118, and 0.405 gram of Ni (as NiSO4-6H2O) were added. A panel was immersed in the solution in a Hull cell and plated. The deposit had some degree of brightness over the entire panel with the area near the middle of the low current density half being considerably brighter, but most of the low current density half was covered with an orange peel surface and was pitted. The solution was altered by adding 0.075 gram of sulfated methyl A panel plated in the altered solution was substantially free of orange peel and pitting, and the deposit on the high current density half and even in the middle of the panel was considerably brighter. Substitution of the sulfated methyl oleate, in separate one 4 liter portions otherwise the same, with ethyl, propyl, butyl, ethylene glycol monomethyl ether oleate sulfate in equivalent proportions produced cadmium plate having a generally similar, but slightly less bright, plate to that produced with sulfated oleate.

What is claimed is:

1. An aqueous cyanide-cadmium plating bath containing at least about 0.01 gram/liter of at least one additive selected from the group consisting of monosulfated monoleate esters, di-sulfated monoleate esters, di-sulfated dioleate esters and sulfated oleic acid.

2. An aqueous cyanide-cadmium plating bath containing from about 0.018 to 0.3 gram per liter of at least one additive selected from the group consisting of monosulfated monoleate esters, di-sulfated monoleate esters, di-sulfated dioleate esters and sulfated oleic acid.

3. An aqueous cyanide-cadmium plating bath containing from about 0.018 to 0.3 gram/liter of at least one additive selected from the group consisting of monosulfated monoleate esters, di-sulfated monoleate esters, di-sulfated dioleate esters and sulfated oleic acid, the alcohol portion of said esters being derived from an alcohol having not more than 2 hydroxy groups and not more than 8 carbon atoms.

4. A process for the electrodeposition of cadmium which comprises the step of electrodepositing cadmium from an aqueous, cyanide-cadmium bath containing at least about .01 gram/liter of at least one additive selected from the group consisting of mono-sulfated monoleate esters, di-sulfated monoleate esters, di-sulfated dioleate esters and sulfated oleic acid.

5. A process for the electrodeposition of cadmium which comprises the step of electrodepositing cadmium from an aqueous cyanide-cadmium bath containing from about 0.018 to 0.3 gram/liter of at least one additive selected from the group consisting of mono-sulfated monoleate esters, di-sulfated monoleate esters, di-sulfated dioleate esters and sulfated oleic acid.

6. A process for the electrodeposition of cadmium which comprises the step of electrodepositing cadmium from an aqueous cyanide-cadmium plating bath containing from about 0.0180.3 gram/liter of at least one additive selected from the group consisting of monosulfated monoleate esters, di-sulfated monoleate esters, di-sulfated dioleate esters and sulfated oleic acid, the alcohol portion of said esters being derived from an alcohol having no more than 2 hydroxy groups and not more than 8 carbon atoms.

References Cited in the file of this patent UNITED STATES PATENTS 1,826,159 Westbrook Oct. 6, 1931 2,113,517 Powell et a1. Apr. 5, 1938 2,383,798 Hull Aug. 28, 1945 

1. AN AQUEOUS CYANIDE-CADMINUM PLATING BATH CONTAINING AT LEAST ABOUT 0.1 GRAM/LITER OF AT LEAST ONE ADDITIVE SELECTED FROM THE GROUP CONSISTING OF MONOSULFATED MONOLEATED ESTERS, DI-SULFATED MONOLEATED ESTERS, DI-SULFATED DIOLEATED ESTERS AND SULFATED OLEIC ACID. 